/**
     * this method used to open Dialog
     */
    private void openDialog(){
        final Dialog dialog = new Dialog(this);
        dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
        dialog.setContentView(R.layout.layout_alert_dialog);
        dialog.getWindow().setLayout(WindowManager.LayoutParams.MATCH_PARENT, WindowManager.LayoutParams.WRAP_CONTENT);

        final EditText etUsername = (EditText) dialog.findViewById(R.id.edit_text_username);
        final EditText etPassword = (EditText) dialog.findViewById(R.id.edit_text_password);
        Button   btnLogin   = (Button)   dialog.findViewById(R.id.button_login);

        dialog.show();

        btnLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if(TextUtils.isEmpty(etUsername.getText().toString())){
                    Toast.makeText(MainActivity.this, "Username is required", Toast.LENGTH_SHORT).show();
                }else if(TextUtils.isEmpty(etPassword.getText().toString())){
                    Toast.makeText(MainActivity.this, "Password is required", Toast.LENGTH_SHORT).show();
                }else{
                    editor = sharedPreferences.edit();
                    editor.putString("username", etUsername.getText().toString());
                    editor.putString("password", etPassword.getText().toString());
                    editor.commit();
                    dialog.dismiss();

                    startActivity(new Intent(MainActivity.this, MainActivity.class));
                    overridePendingTransition(0,0);
                    finish();
                }
            }
        });
    }